Advances in multi-dimensional super-resolution nonlinear optical microscopy

In this review, recent advances toward bridging the mismatching length scales of optical spectroscopy and imaging are described. Spectroscopic measurements that span ultraviolet to infrared wavelengths provide rich details about the structural properties of molecules and materials. However, the diffraction limit precludes the spatial resolution needed to image these systems commensurate with structure. Many groups have innovated statistical approaches that allow an optical point source to be determined, or ‘localized,’ with a precision that approaches the molecular length scale. As we review here, interferometric nonlinear optical imaging (INLO) allows researchers to simultaneously acquire spectroscopic data and localize the point source in three dimensions with nanometer precision using a single wide-field microscope. Employing plasmonic nanoparticles as prototypical systems, we show that INLO yields sample excitation spectrum, coherence lifetimes (i.e. homogeneous linewidth), and polarization-dependent responses. The INLO method can also be used for polarization-resolved (e.g. circular dichroism) imaging. Hence, multiple dimensions of spectroscopic information content can be added to the optical image. A discussion of prospects for extending the INLO-localization platform to other so-called super-resolution spectroscopy measurements is also provided.